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Working with interpolation

From: Scanning Techniques for Photography, Art, and Design

Video: Working with interpolation

Here I would like to discuss the difference between and the significance of Optical Resolution versus Interpolated Resolution. I've opened up an image of an O that I've scanned with my scanner at a resolution of 1200 pixels per inch. I chose 1200 pixels per inch for two reasons. One, it gives me enough detail that I can get a really sharp consistent edge as we'll see, but I also know that this is the optical also known as hardware resolution of the scanner. What that means is that the scanner is actually set up to actually physically capture pixels at one- 1200th of an inch on the side.

Working with interpolation

Here I would like to discuss the difference between and the significance of Optical Resolution versus Interpolated Resolution. I've opened up an image of an O that I've scanned with my scanner at a resolution of 1200 pixels per inch. I chose 1200 pixels per inch for two reasons. One, it gives me enough detail that I can get a really sharp consistent edge as we'll see, but I also know that this is the optical also known as hardware resolution of the scanner. What that means is that the scanner is actually set up to actually physically capture pixels at one- 1200th of an inch on the side.

So this is going to capture 1200 pixels in every inch horizontally and 1200 pixels in every inch vertically. The reason why this is important will become clear in just a moment. So this is a 1200 pixel print scan and I'm going to zoom in on this so we can take a look at these two edges right here and you'll notice there is a real consistency to the placement of pixels. There is a little missteps every once in a while, but in general this is very, very consistent edge and the same thing on the inside. What I'm going to do now is I'm going to make a duplicate copy of this image and I'm just going to label this 1700 and we're going to convert this image from a 1200 pixel per inch image to a 1700 pixel per inch image in Photoshop.

Notice a couple of things, one is, by default and I'm leaving it that way I'm re-sampling this image, watch what happens when I resample this image from the 1200. The original pixel dimension is 540x442, when I go up to 1700 the number of pixels goes from 765 to 626. We're adding pixels, we're adding them by interpolating, by using the pixels that are already there to create more pixels, this is what interpolation does. I'm going to click OK and then I'm going to reposition this so we can see these pixels in the same place that we see them here.

Now let's compare and in fact contrast these two different edges. Look at this very, very nice smooth consistent edge and look what's happened to this edge, do you see how much rougher it is? It's even worse on the inside, and that's just one step of interpolation from 1200 to 1700, we haven't rotated or skewed or done anything. And what this demonstrates is that if you interpolate your image either during the scan or in the post scan you're going to lose edge quality, the quality of your image is going to go down, because new pixels are created from old pixels and they're never as good as the original ones.

This is particularly important if in the very beginning phases you decide oh I want this line art image, in this case this O to be converted into vectors. When we do a conversion of vectors the vectorization software loops the consistency of this edge and the smoother and more consistent the edge is the higher the quality of the vector the smoother the vector is going to be. But the same thing is true for continuous tone images, the more you resample them the lower the quality they're going to be, they're going to lose sharpness, they're going to lose definition. So our general rule of thumb is we want to avoid interpolation whenever possible, and what this involves is scanning, using the optical resolution of the scanner whenever we can.

And in the case of vectors and we'll return to this later wait until you've converted your images into vectors before you do any geometric manipulation of them. Because remember as long as you've got pixels and you're doing geometric manipulation the quality of your edges are going to be lost. There are some cases where you actually can embrace the enemy where you've got damaged images, where you can actually use this interpolation to your benefit to kind of smooth out some of the damages, but as a general rule we want to avoid interpolation whenever possible and as far as scanning goes that means setting the proper resolution to begin with.

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This video is part of

Image for Scanning Techniques for Photography, Art, and Design
Scanning Techniques for Photography, Art, and Design

58 video lessons · 8275 viewers

Taz Tally
Author

 
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  1. 6m 48s
    1. Welcome
      1m 11s
    2. What you should know before watching this course
      3m 54s
    3. Using the exercise files
      1m 43s
  2. 1h 0m
    1. Scanners and digital cameras
      3m 6s
    2. Types of scanners
      5m 2s
    3. Scanner location
      3m 19s
    4. What scanners and digital cameras create
      7m 22s
    5. Understanding grayscale values and channels
      3m 19s
    6. Understanding pixels and vectors
      4m 1s
    7. Choosing pixels or vectors
      2m 27s
    8. Resolving resolution
      6m 32s
    9. Working with interpolation
      3m 31s
    10. Understanding the effects of compression
      2m 4s
    11. Evaluating and correcting images with histograms
      8m 26s
    12. Saving to different file formats
      7m 4s
    13. Color management
      4m 23s
  3. 33m 22s
    1. Cleaning your scanner
      7m 31s
    2. Cleaning your images
      7m 47s
    3. Calibrating your scanner
      9m 13s
    4. Creating and applying a color management profile
      8m 51s
  4. 20m 55s
    1. Evaluating your scan challenges
      9m 46s
    2. Reproducing vs. assigning colors
      6m 20s
    3. Recognizing continuous tone (contone) vs. dot pattern images
      4m 49s
  5. 36m 32s
    1. Understanding bit depth
      8m 49s
    2. Selecting a scan mode
      8m 20s
    3. Sharpening and its effects
      10m 40s
    4. Creating and assigning color management profiles
      8m 43s
  6. 2h 25m
    1. Taking the Tazmanian Oath!
      3m 38s
    2. Choosing your weapon
      4m 2s
    3. Setting up your scanning preferences
      12m 14s
    4. Performing a prescan
      2m 53s
    5. Assigning a scan frame
      5m 40s
    6. Determining scan resolution
      7m 57s
    7. Choosing a scan mode and bit depth
      5m 53s
    8. Naming images
      1m 49s
    9. Scanning simple logos and line art
      12m 21s
    10. Scanning complex line art
      7m 33s
    11. Scanning grayscale contones
      13m 22s
    12. Scanning color contones
      13m 54s
    13. Sharpening
      9m 39s
    14. Scanning printed/screened or patterned images
      7m 1s
    15. Scanning positive transparency film
      12m 33s
    16. Scanning negative transparency film
      9m 11s
    17. Capturing high dynamic range (HDR) scans
      1m 47s
    18. Setting up wet scans
      14m 29s
  7. 1h 48m
    1. Scanning, converting, and using simple line art
      5m 32s
    2. Scanning and using detailed line art
      10m 52s
    3. Scanning landscapes
      15m 50s
    4. Scanning product shots
      11m 58s
    5. Scanning combo/complex images
      9m 3s
    6. Adjusting distressed images
      11m 12s
    7. Scanning images with no neutrals
      11m 57s
    8. Post-scan touch-ups
      2m 7s
    9. Scanning images for multiple uses
      10m 44s
    10. Automatic scanning
      10m 40s
    11. Streamlining big jobs with batch scanning
      5m 22s
    12. Using your manufacturer's scanning software
      3m 14s
  8. 27s
    1. Goodbye
      27s

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